The utilization of sheet metal louvers in ducts or conduits, such as air-conditioning or other fluid ducts, usually requires that the louvers be pivoted or turned about an axis perpendicular to the axis of the duct. The pivoting of each of the louvers results in an adjustment of the air flow or fluid flow through the duct. Typically, louvers of the prior art have incorporated piano wire hinges or various equivalents thereto as the mechanical means permitting the pivoting of the individual louvers. The prior art has also included the utilization of hinge pins in the form of short metal cylindrical dowels that are secured to the edge of a louver in a variety of ways such as by mechanically clamping, rivoting or staking.
In many ventilation applications, such as evaporative cooling, it is frequently desirable to provide a duct having automatic louvers positioned therein. In the latter circumstances, the louvers will normally be maintained in a closed position simply through the force of gravity on each of the louvers. When cooled air is to enter a room or exhaust air is to be permitted to escape from the room, the air pressure within the duct is sufficient to cause the louvers to open and permit the passage of air into the dwelling or exhaust air to the atmosphere. When the system has been turned off, and the transmission of air through the duct is no longer desired, it is important that the louvers shut and effectively seal the duct. This sealing of the duct against reverse flow is effected by the tolerances permitted between the edges of the pivoting louver and the side wall of the duct or conduit as well as the contacting surfaces of adjacent louvers. The hinge pin utilized with the louver thus becomes an important element in the proper operation of each of the louvers. The louver must obviously be permitted to rotate or pivot without excessive force while nevertheless appropriately assuming its closed position when the force of escaping air is removed from the surface of the louver.